The present invention relates generally to a high speed mailing machine which includes a postage meter for applying a postage indicia to mail pieces passing through the mailing machine. More particularly, the present invention relates to an improved inking device in the postage meter for continuously applying ink to the printing plate of the meter.
In a typical high speed mailing machine, mail pieces in the form of envelopes are fed seriatim along a feed deck by suitable feeding devices past a plurality of working stations which usually include an envelope flap opening device, a flap moistening device, a flap closing and sealing device, a postage meter, and a stacking device. The mailing machine may also include a scale for weighing the mail pieces before they pass through the postage meter. A principal advantage of such machines is that they can perform the aforementioned operations on mail pieces at a very high rate of speed, in the order of three to four mail pieces per second, and therefore are very attractive to high volume mailers such as credit institutions, telephone companies, telemarketing operations, etc.
One of the major problems in maintaining a high speed mailing machine operational is to prevent the leakage of ink from the printing device of the postage meter. Typical postage meter ink is a relatively free flowing liquid which can ooze through very minute openings if the device normally containing the ink does not maintain adequate seals to prevent such leakage. Also, typical postage meter ink has rather caustic properties and can cause considerable damage to surrounding parts of the machine if it should leak from the printing device and contact other parts of the machine. Still further, any mailing machine in which ink leaks and contacts parts of the postage meter which in turn contact the mail pieces and thereby transfer unwanted ink to the mail pieces would be commercially unacceptable and not a viable product. And since mailing machines of the type in which the present invention is found are expected to operate for hundreds of thousands of cycles without the necessity for major service, it becomes absolutely critical to the success of such a machine that the postage meter ink be completely contained except for that which is applied to the printing die of the postage meter during normal operation of the mailing machine.
In the development of the printing device for the high speed mailing machine, two significant problems dealing with leakage of ink were encountered and had to be overcome. One was the manner in which the inking device was constructed in order to maintain an effective seal between an ink pad formed of an absorbent material and an ink reservoir device which contained the ink pad. In the type of printer used in the postage meter, a large flat area of the ink pad had to be exposed to contact the exposed face of a printing die, and the problem that was confronted was how to prevent ink from escaping around the outer edge of the ink pad and flowing over parts of the inking device and thereby causing the problems mentioned above.
An early form of inking device that was incorporated in the mailing machine during early development stages is shown in the U.S. Pat. No. 5,056,433 issued Oct. 15, 1991, in which a generally rectangular ink pad is contained in a flat, also generally rectangular tray and is secured therein by a cover member having an aperture through which a substantial portion of the upper surface of the ink pad is exposed to contact the printing die, and which presses against a peripheral flange portion of the ink pad to secure it in the tray. The bottom surface of the tray is provided with elongate ribs to provide flow channels for the ink so that it can reach and saturate all portions of the ink pad to maintain and even distribution of ink therein and transfer a uniform amount of ink over the surafce of the printing die. This is critical in order to meet the requirements of the U.S. Postal Service regarding the quality of indicia printed by postage meters. The ends of the ribs were provided with ramp portions which slanted upwardly toward the outer side walls of the tray so as to urge the adjacent portions or the ink pad against the underside of the cover member to provide a seal to prevent ink from leaking between the upper surafce of the ink pad the the lower surafce of the cover. Additional short ribs having upwardly slanting upper surfaces were also provided along the end edges of the tray to provide the same function along the ends of the ink pad.
After long periods of test operation, it was found that, although the inking device shown in said prior application performed very well from the standpoint of maintaining a continuous and proper amount of ink to the ink pad for normal operation of the mailing machine, it was very susceptible to leakage problems caused by several factors, and that over an extended period of operation, very substantial amounts of ink would leak from the space between the upper surface of the flange portion of the ink pad the lower surface of the cover member intended to confine the pad in the ink tray. It was found that the reason for the leakage was that the edge portions of the ink pad, that is the peripheral flange portion on all sides of the ink pad, were sliding down the upwardly slanting ramp portions of the ribs formed in the bottom of the ink tray, thereby defeating the effect of these slanted portions which were intended to maintain the flange portions of the ink pad in firm contact with the underside of the lid to provide an effective ink seal. One reason why the leakage of ink was so great is that the ink is pumped into the reservoir under pressure to assure a constant flow of ink along the channels formed by the ribs in the tray; without an effective seal between the ink pad and the cover member, the ink is more inclined to flow out of the tray rather than along the channels, since it will take the path of least resistance. The more the edge portions of the ink pad slid down the ramp portions of the ribs, the greater was the rate of leakage of ink during operation of the machine. Thus, it became necessary to prevent any movement of the edge portions of the ink pad down the slanted portions of the ribs during operation of the machine.
In order to understand the reasons why the edge portions of the ink pad to creep down the slanted portions of the ribs during operation of the mailing machine, it is necessary to understand the forces imposed on the ink pad during each cycle of operation. One of the limiting factors in maintaining high speed operation of such mailing machines is the speed with which the printing plate of the postage meter can be reinked after each cycle of operation. Reinking after each printing cycle is necessary in order to consistently print a sharp, uniform indicia on each envelope which will pass the rigid print quality standards of the U.S. Postal Service. Thus, during each printing cycle the printing die of the postage meter is inked by the inking device which normally is dispose in a home position, and which is extended laterally to an operative position. In this position, the inking device is moved upwardly to press an ink pad against the underside of the printing die which applies the postage indicia to the envelopes as they are fed through the postage meter. Immediately after being pressed against against the printing die, the inking device is lowered and retracted to its home position, after which the printing operation takes place. Thus, during each cycle of operation, the inking device moves from a home position laterally of the direction of envelope movement to the operative position, then upwardly to ink the printing die, then downwardly, and finally laterally back to the home position.
When it is considered that the mailing machine with which the present invention is concerned is capable of handling three to four mail pieces per second, it becomes apparent that the foregoing cycle of operation of the inking device occurs at a very high rate of speed, with successive movements of the inking device being measured in milliseconds. A typical cycle of operation requires about 100 ms, of which only 40 ms are required for actual movement of the inking device, the other 60 ms occurring while the inking device is stationary. Thus, the movement of the inking device during each cycle of operation is characterized by extremely rapid acceleration and deceleration between successive increments of movement, which produces about three to four Gs of force on the various parts of the inking device. These forces are sufficient, over a extended period of operation, to cause the edge portions of the pad to creep down the slanted portion of the ribs, thereby resulting in the serious ink leakage problems described above.